<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>

<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .list {
            width: 200px;
            height: 150px;
            background-color: aqua;
            overflow: auto;
        }

        .news {
            height: 30px;
        }
    </style>
</head>

<body>
    <!--准备好一个"容器"-->

    <div id="test">

    </div>

    <!--引入库-->
    <script type="text/javascript" src="../js/react.development.js"></script>
    <script type="text/javascript" src="../js/react-dom.development.js"></script>
    <script type="text/javascript" src="../js/babel.min.js"></script>


    <script type="text/babel">
        class NewsLisst extends React.Component {


            state = {
                newArr: []
            }

            componentDidMount() {
                setInterval(() => {
                    const { newArr } = this.state;
                    const news = '新闻' + (newArr.length+1) ;
                    this.setState({ newArr: [news, ...newArr] });
                }, 1000);
            }

            getSnapshotBeforeUpdate(){
               return this.refs.list.scrollHeight;
            }


            componentDidUpdate(prevProps,prevState,snapshot){
                this.refs.list.scrollTop += this.refs.list.scrollHeight -snapshot;
            }

            render() {
                return (
                    <div className="list" ref="list">
                        {this.state.newArr.map((item,index)=>{
                            return <div className="news" key={index}>{item}</div>
                        })}
                    </div>
                );
            }
        }

        ReactDOM.render(<NewsLisst />, document.getElementById('test'));
    </script>

</body>

</html>